1. Field of the Invention
The present invention generally relates to an image forming apparatus which uses a toner supplying device for supplying toners contained in a toner container to a developing device.
2. Description of the Related Art
In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunctional peripheral combining the above functions, a toner supplying device is publicly known in which toners contained in a toner container are supplied to a developing device at a position apart from the toner container (for example, in Patent Document 1).
In Patent Document 1, a toner container (toner bottle) which contains toners is detachably disposed from an image forming apparatus main body, and a developing device (process cartridge) is at a position apart from the toner container. In addition, a toner supplying device (toner carrying device) is between the toner container and the developing device. The toner supplying device provides a toner tank (sub hopper) which stores toners supplied from the toner container and a toner supplying pipe which supplies the toners contained in the toner tank to the developing device. The toner supplying pipe carries the toners in an obliquely downward direction and supplies the toners to the developing device. In addition, a carrying coil is inside the toner supplying pipe. That is, the toner supplying pipe carries the toners in the obliquely downward direction by using a toner carrying force of the carrying coil and toner own weight.
The toner supplying device suitably supplies the toners to the developing device corresponding to a consumed toner amount in a developer in the developing device.
In the image forming apparatus, it is not necessary for the toner container to be adjacent to the developing device. Therefore, the device design freedom is high and the image forming apparatus can be small sized.
In Patent Document 2, an image forming apparatus is disclosed. The image forming apparatus provides a cylinder-shaped toner container (toner cartridge). The toner container includes a spiral groove in an inner wall of a main body of the toner container. Then toners are discharged from a toner supplying opening of the main body of the cylinder-shaped toner container while rotating the main body.
Specifically, two protrusions are formed on the bottom surface of the main body of the toner container. The two protrusions have a 180-degree distribution angle with the rotational axle center of the main body as the reference. When the toner container is attached to the main body of the image forming apparatus, two claw members of a drive coupling on the main body of the image forming apparatus engage the corresponding protrusions of the toner container, and the toner container is rotated.
When the toner container is rotated, the toners are discharged from an opening of the main body of the toner container. The toners discharged from the opening of the main body of the toner container are carried to the developing device and are consumed in a developing process.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2004-139031
[Patent Document 2] Japanese Laid-Open Patent Application No. 2003-330247
However, in Patent document 1, in some cases, the amount of toners supplied to the developing device is varied.
Since the toners are carried in the obliquely downward direction in the toner supplying pipe, when the supply of the toners to the developing device is stopped, even if the carrying coil is stopped, the toners remaining in the toner supplying pipe drop into the developing device due to the toner own weight. That is, in many cases, the amount of the toners more than a target amount is supplied to the developing device. In this case, the concentration of the toners in the developer (the ratio of the toners to the developer) becomes greater than a target concentration, the image density of an output image may be high, toners may be scattered, and the background image may be degraded due to lowering a toner charging amount.
In order to solve the above problem, by considering that an excessive amount of toners is supplied to the developing device after stopping the carrying coil, it can be assumed that the toner carrying force of the carrying coil is determined to be lower than a predetermined value beforehand. However, in this case, while the carrying coil is driven, the amount of toners to be supplied to the developing device may be insufficient, the image density of the output image may be lowered, and the developer may be adhered onto an image carrier or the output image.
Even if the toner supplying pipe is disposed in the horizontal direction, the above problem occurs. That is, when the toners are supplied to the developing device from the opening of the toner supplying pipe by using the toner own weight after carrying the toners in the horizontal direction, remaining toners near the opening may be dropped by the toner own weight right after stopping the carrying coil. Especially, when the liquidity of the toners is high, this problem remarkably occurs.
In Patent Document 2, when the main body of the toner container is rotated, in some cases, the amount of toners supplied to the developing device is varied due to a large load fluctuation for driving the main body.
The inventor of the present invention has studied several times about the load fluctuation and has found the following results. That is, the two protrusions formed on the bottom surface of the main body of the toner container are formed with the 180-degree distribution angle. When the toner container is attached to the main body of the image forming apparatus, the two claw members of the drive coupling repeat movements in which one claw member reaches a vertical status and the other claw reaches a horizontal status at the same timing. Consequently, when the main body of the toner container is driven, the load fluctuation becomes great.
In addition, when a driving source of the drive coupling is also used to drive a toner carrying screw which carries toners discharged from the toner container, in addition to driving the toner container, the load fluctuation may occur. Further, when a general-purpose DC motor which is normally used to build a plastic model is used as the driving source for lowering the cost, the load fluctuation remarkably occurs.